Whorled Rosinweed, Three-leaved Rosinweed - Silphium trifoliatum

Silphium trifoliatum - Whorled Rosinweed, Three-leaved Rosinweed. Silphium triofliatum is listed as a variety of S. asteriscus in Flora of North America, but ITIS continues to list it separately, although no longer with varieties, formerly var. trifoliatum and var. latifolium. Var. latifolium has opposite rather than whorled leaves. I expect that when all the updating is done, S. trifoliatum will be gone, and listed only as varieties of S. asteriscus.

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Site: Wilson County, TN Date: 2012-August-04

Photographer: Gerald C. Williamson Nikon D7000Tamron AP AF 90MM Macro

Whorled Rosinweed has 8 to 13 yellow ray flowers. The ray flowers of Silphium develop the seeds; the disk flowers are sterile.

Site: Wilson County, TN Date: 2012-August-04

Photographer: Gerald C Williamson Nikon D7000Tamron AP AF 90MM Macro

Whorled Rosinweed grows to about 6 feet tall and has leaves all the way to the inflorescence.

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Site: Wilson County, TN Date: 2012-August-04

Photographer: Gerald C Williamson Nikon D7000Tamron AP AF 90MM Macro

The smooth, usually glaucous stem of Silphium trifoliatum has mostly whorls of 3 leaves - occasionally opposite or rarely a whorl of 4 - which are nearly sessile (very short petioles) and narrowly ovate. The leaves have very shallow teeth or may be entire. Silphium brachiatum is similar, but with opposite lanceolate leaves having cordate or truncate bases, and fewer ray flowers. The distribution of S. brachiatum is also much smaller, being limited to a few counties in Alabama, Georgia, and Tennessee.